Exemplary embodiments of the present invention are directed to a mold and a production device for production of fiber-reinforced components by means of an injection process and a method for production of fiber-reinforced components by means of an injection process.
Dry fibrous semi-finished products are generally infiltrated with a matrix material and cured in the injection process. Such methods are also referred to as liquid resin infusion (LRI) methods. The fibrous semi-finished products can be formed from carbon fibers (CF-reinforced plastics), glass fibers (GF-reinforced plastics), aramid fibers (AF-reinforced plastics), boron fibers (BF-reinforced plastics) or hybrid materials and from corresponding fabrics or lays.
A known method for producing fiber-reinforced components by means of an injection process is described in German Patent Document DE 100 13 409 C1. In this case a fibrous semi-finished product is placed on a mold. A flow aid is arrange on the surface of the fibrous semi-finished product and a first space is formed by providing a gas-permeable and matrix material-impermeable membrane around the fibrous material and the flow aid. The second space is formed around the first space by arranging a gas- and matrix material-impermeable film and it is sealed against the mold. The flow aid is connected to a supply vessel for the matrix material. A vacuum line extends into the second space. A partial vacuum is now applied via the vacuum line, the matrix material is drawn in from the supply vessel into the flow aid by the resulting pressure difference, i.e., injected into the first space, and distributed over the fibrous semi-finished product. The matrix material impregnates the fibrous semi-finished product and cures. The air-permeable but matrix material-impermeable material membrane prevents matrix material from penetrating into the second space and therefore into the vacuum line but at the same time permits suction of the air found in the matrix material and fibrous semi-finished products. The matrix material can then cure without air inclusions and high-grade fiber-reinforced components can be produced.
An improvement of this process control can be achieved by the arrangement described in German Patent Document DE 101 401 66 B4, which includes pressure control means that generate a partial vacuum in the supply vessel toward the end of the injection phase or after it and in so doing create better controllability of the process and the component quality.
A device for improved degassing of a fibrous semi-finished product and the matrix material is described in German Patent Document DE 102 03 975 C1. Here a barrier layer impermeable for the matrix material is arranged in the first space above the first flow aid and an additional flow aid provided on it. In the area in which the barrier layer is situated between the first and second flow aid, a gate device is applied to the second flow aid, via which the matrix material is injected into the first space. When a partial vacuum is applied, the matrix material now initially flows into the second flow aid, in which case air present in the matrix material and fibrous semi-finished product can escape because of the applied partial vacuum. The barrier layer then prevents the matrix material from coming into contact with the first flow aid in the area of the gate device. The matrix material therefore initially passes through the second flow aid in the horizontal direction. The barrier layer is arranged so that the first and second flow aids come in contact at a location away from the gate device. The matrix material at this location comes in contact with the first flow aid and is distributed over it. From there it is further conveyed in the thickness direction to the fibrous semi-finished product and impregnates it. The extended path of the matrix material by means of the barrier layer through the evacuated volume of the first space means that the air present in the matrix material and in the fibrous semi-finished product initially escapes before it impregnates the fibrous semi-finished product. Air inclusions can thus be further reduced and the quality of the components further increased.
German Patent Document DE 101 56 123 B4 describes a structure by means of which a prepreg semi-finished product, which is already impregnated with resin, is joined to a textile semi-finished product to be impregnated with matrix material.
A common feature of all these devices and methods is that, before the beginning of the process, a demanding structure consisting of the puller, flow aid and the gas-permeable and matrix material-impermeable membrane must initially be produced to form a first space.
An improvement is therefore proposed in German Patent Document DE 10 2008 006 261 B3 in which a gas-permeable but matrix material-impermeable membrane is described, on which a flow aid is laminated and puller arranged. By provision of such a multifunction laminate only one layer to form the first space need be arranged above the fibrous semi-finished product. This significantly simplifies the process layout.
In order to be able to also produce components with different curvatures and/or torsions, German Patent Document DE 10 2008 028 865 A1 describes the provision of a bendable or twistable fibrous semi-finished product.
It is also common to the aforementioned devices and methods that a gas- and matrix material-impermeable film and a spacer are arranged above the gas-permeable and matrix material-impermeable membrane to form the second space. In addition, further molds are sometimes provided above the gas- and matrix material-impermeable membrane to form a shaped inside surface of the fiber-reinforced component. In particular, the preparation of this structure entails significant manual expense in large components with a complex internal contour.
Exemplary embodiments of the present invention are directed to production of fiber-reinforced components by means of an injection process with a less complicated and demanding structure.
Exemplary embodiments of the present invention are directed to a mold for production of fiber-reinforced components by means of an injection process has a mold surface to form a surface of the fiber-reinforced component with a partial area and a second partial area. The mold has an injection area for injection of matrix material and a fibrous material situated on the mold surface through the second partial area of the mold surface and an evacuation area for evacuation of a mold volume through the first partial area of the mold surface, in which the mold volume is limited by the mold.
Both the matrix material feed and the vacuum line are therefore advantageously introduced to the mold and a complicated and demanding structure becomes unnecessary in the devices just described. The method can therefore be significantly simplified.
In a preferred embodiment a puller for easier removal of the mold from a fiber-reinforced component is arranged on the mold surface. This puller, after curing of the matrix material introduced into the fibrous material, permits the mold to be advantageously removed easily from the surface of the fiber-reinforced component so formed.
The first partial area of the mold surface also preferably has a semi-permeable membrane for passage of gases and for retention of matrix material. The semi-permeable membrane makes it possible for gases to be removed from the mold volume by applying a vacuum to the evacuation area, in which case the matrix material is simultaneously retained in the mold volume. Accordingly, matrix material cannot penetrate into the evacuation area and clog it and thus make it ineffective.
The semi-permeable membrane and the puller are preferably formed as a composite in the first partial area of the mold surface. By using a composite only one step is necessary to position the membrane and puller, whereas otherwise two individual blanks must be applied to the mold. This composite is advantageously fixed with a peripheral adhesive to the mold surface. The peripheral adhesive is provided, on the one hand, to fasten the composite and, on the other hand, prevents liquid material from flowing over the edge into the evacuation area. The peripheral adhesive can preferably also be used to fasten and seal individual blanks of the semi-permeable membrane and/or the puller.
Flow aids for better distribution of the injected matrix materials are advantageously provided in the second partial area of the mold surface. The matrix material can therefore preferably be distributed quickly and uniformly over the fibrous material. A combination of one or more point or linear gates with a flat distribution medium can be applied, for example, an open-structured textile on the mold surface. Because of this the matrix material is preferably distributed with comparatively limited flow resistance over the fibrous material surface and essentially impregnates the fibrous material in the thickness direction. Channels and/or a groove pattern can advantageously be provided to distribute the matrix material in the second partial area of the mold surface so that additional aids in the form of gate channels or flat flow aids can be saved. The integrated matrix distribution is preferably configured so that it is impressed as little as possible into the surface of the fiber-reinforced component.
In a preferred embodiment flow aids are arranged in the first partial area for better evacuation of the mold volume. In order to advantageously provide adequate air supply in the first partial area of the mold surface it is advantageous if appropriately dimensioned flow aids are provided in the first partial area of the mold surface. These can be formed preferably as grooves. As an alternative, however, a textile, for example, a woven fabric, knit fabric, nonwoven or mesh can be provided in the first partial area of the mold surface.
The flow aids and/or the stream aids are therefore formed on a mold surface advantageously as grooves, channels, woven fabric, nonwoven, knit fabric or mesh.
In a particularly preferred variant the first partial area of the mold surface and the second partial area of the mold surface are formed in partial molds separate from each other but connectable to each other. It is thus advantageously possible, depending on the desired fiber-reinforced component, to provide an individual number of evacuation areas and injection areas on the mold.
A connection device for a tight connection of the partial molds is preferably provided. By means of a connection device the partial molds separated from each other can preferably be joined together vacuum-tight. The connection device can then preferably be formed from a flexible adhesive or sealing strip, a liquid or gel-like sealant, from profile seals glued onto the partial molds or introduced to them or from flexible sealing lips applied to the partial molds or integrated in them.
Due to the fact that preferably partial molds are provided with different areas, namely the injection or evacuation area, the mold can be constructed to form the fiber-reinforced component in preferably modular fashion. Because of this both different components and different component sizes can be achieved using the same partial molds.
A production device for production of fiber-reinforced components by means of an injection process advantageously has a mold with a mold surface to form a surface of the fiber-reinforced component and a vacuum device to evacuate a mold volume at least partially limited by the mold surface, within which the injection process is performed. The production process also has an injection device for injection of matrix material into the mold volume in order for a fibrous material arranged within the mold volume to penetrate into the area of the mold surface.
The injection device preferably has a matrix distribution device to distribute a matrix material. The matrix distribution device includes, on the one hand, lines that supply the matrix material over different sites of the fibrous material and, on the other hand, a supply vessel to store the matrix material. If the vacuum device now generates a vacuum, the matrix material is drawn into the lines by the pressure difference from the supply vessel and finally into the mold volume by the injection device. There it impregnates the fibrous material.
The injection area preferably has matrix lines for connection to the injection device. The matrix material can thus be guided simply to the injection area from a matrix material supply vessel.
The evacuation area also advantageously has vacuum lines for connection to the vacuum device. The evacuation area can therefore be simply connected to a vacuum pump.
A surrounding closure device to define the mold volume to be evacuated is preferably provided on the mold.
The closure device preferably separates the surroundings from the mold volume in the mold into which the fibrous material is introduced. The closure device is advantageously designed so that the mold volume is closed vacuum-tight relative to the surroundings. The closure device is preferably designed flexible in order to be able to compensate for any shifts that occur during the production process for the fiber-reinforced component, for example, by compaction of the fibrous material under vacuum or during infusion of the matrix material or because of thermal expansion. The closure device therefore can advantageously be a flexible adhesive or sealing strip, a liquid or gel-like sealant, a profile seal glued onto the mold or introduced to it or flexible sealing lip applied to the mold or integrated in it.
In a method for production of fiber-reinforced components by means of an injection process with the steps                Arrangement of fibrous material in a mold volume, which is limited at least on one side by a mold surface of a mold,        Evacuation of the mold volume and injection of matrix material into the mold volume,        Injection of the matrix material into the mold volume is carried out through a second partial area of the mold surface and evacuation of the mold volume is carried out through a first partial area of the mold surface.        
Accordingly, this avoids the complicated arrangement of two spaces above the fibrous material and the design is significantly simplified.
Evacuation of the mold volume advantageously occurs through a semi-permeable membrane arranged on the mold surface. The semi-permeable membrane is advantageously configured so that it allows gases to pass through but retains the matrix material. Therefore no matrix material can penetrate into the evacuation area, i.e., the first partial area of the mold surface, and clog it. Preferably the mold surface is formed by connecting at least two partial molds designed separate from each other. Because of this it is possible to flexibly construct the mold surface, which images the surface of the fiber-reinforced component during the process, from several partial molds and thus achieve flexibility with respect to component shape and size.
During production of fiber composite components by means of the vacuum-assisted process (VAP) a significant manual expense for process preparation has thus far been required. The invention, which is explained below in a practical example, serves for automation of the infusion structure.
A typical VAP structure is characterized by a fiber blank situated in a one-sided mold, i.e., the fibrous material, aids to distribute the fibrous material in the form of resin, a microporous semi-permeable membrane arranged above it and a vacuum sack enclosing the structure whose film is gas- and matrix-impermeable. Molds (clamping pads) are also locally provided partially on the membrane and vacuum sack. It is easy to comprehend that the preparation of this structure entails significant manual expense, especially in large components with complex inside contour (for example, spherical, with stiffening, etc.). It is sometimes required to integrate distribution of the matrix material in the form of appropriately dimensioned channels and grooves in the mold and/or clamping pads, but error-free mounting and sealing of the two films (membrane and vacuum film) one above the other is still a problem.
In an advantageous embodiment of the invention the suction side with membrane, vacuum distribution and vacuum connections is therefore also integrated in the clamping pads. The inside of the component is almost completely covered with these clamping pads (or alternates with them and those with integrated resin distribution). Sealing of the vacuum structure is then only required between the clamping pads and along the component edge, if not even a sealing cord or sealing lip (for example, made of silicone) is sufficient. The clamping pads on the suction side can be prepared in a separate workplace (also easily automated in the case of simple geometry (for example, constant width)) and positioned on the infusion structure with a corresponding device.
A drastic reduction of manual expense and a reduction in throughput and mold occupation times can be achieved on this account.